There is no Common! The closest you get is English, but even that is highly sporadic on the lost colonies. This is due to the long isolation most colonies endured. If the colonists were 92% Chinese and all non-Chinese spoke Chinese, It is safe to assume Chinese is the language of the colony. Even if 33% of said colony also spoke Russian, chances are after two or three generation with little or no need for, or value seen in, the language, it would die out or become increasingly rare. Languages will be important, so think of your background and make your choices wisely.
In the TPC, English, Chinese, and Russian are the most common, followed by German, Japanese, Spanish.
Defiant Worlds: German, English, Russian are the most dominant.
The lost worlds were mostly Chinese, Russian, and English speaking cultures, but the time away from the core worlds has allowed the dialects to shift substantially.
Read/Write Language and Speak Language are now a single skill: Language (None). Like Craft or knowledge, there is a separate skills for each language. A character can have up to four ranks in a Language. The character is considered to have 4 ranks in her native language. The first rank in a language means the character can use a few basic words, or has an equivalent to basic level classes. A second rank represents the ability to have a conversation, but clearly it is not her native tongue and struggles to keep up. With a third rank, a character displays impressive conversation skills and is considered fluent. She can distinguish different dialects and identify class level (if the language includes that). With 4 ranks, the language is considered like a second native language. Others who are native to the language are almost unable to distinguish her accent from their own.